Re-hydration antenna for ablation

ABSTRACT

A system for use with a microwave antenna includes a microwave antenna configured to deliver microwave energy from a power source to tissue and a sensor module in operative communication with the power source and configured to detect a reflectance parameter. The system further includes a jacket adapted to at least partially surround the microwave antenna to define a fluid channel between the jacket and the microwave antenna. A plurality of fluid distribution ports are defined through the jacket and are in fluid communication with the fluid channel to permit the flow of fluid through the jacket. The system further includes a fluid pumping system operably coupled to the power source and configured to selectively provide cooling fluid to the fluid channel for distribution through the fluid distribution ports based on the reflectance parameter.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of U.S. patentapplication Ser. No. 12/413,023, filed on Mar. 27, 2009, which claimspriority to U.S. Provisional Application No. 61/041,072 filed on Mar.31, 2008, the entire contents of each of which are incorporated hereinby reference.

BACKGROUND

1. Technical Field

The present disclosure relates generally to devices that may be used intissue ablation procedures. More particularly, the present disclosurerelates to devices and methods for maintaining ablation temperaturessurrounding microwave antennas radiofrequency probes during ablationprocedures.

2. Background of Related Art

In the treatment of diseases such as cancer, certain types of cancercells have been found to denature at elevated temperatures which areslightly lower than temperatures normally injurious to healthy cells.These types of treatments, known generally as hyperthermia therapy,typically utilize electromagnetic radiation to heat diseased cells totemperatures above 41° Celsius while maintaining adjacent healthy cellsat lower temperatures where irreversible cell destruction will notoccur. Other procedures utilizing electromagnetic radiation to heattissue also include ablation and coagulation of the tissue. Suchablation procedures, e.g., such as those performed for menorrhagia, aretypically done to ablate and coagulate the targeted tissue to denatureor kill the tissue. Many procedures and types of devices utilizingelectromagnetic radiation therapy are known in the art. Such therapy istypically used in the treatment of tissue and organs such as theprostate, heart, kidney, lung, brain, and liver.

Presently, there are several types of microwave probes in use, e.g.,monopole, dipole, and helical, which may be inserted into a patient forthe treatment of tumors by heating the tissue for a period of timesufficient to cause cell death and necrosis in the tissue region ofinterest. Such microwave probes may be advanced into the patient, e.g.,laparoscopically or percutaneously, and into or adjacent to the tumor tobe treated. The probe is sometimes surrounded by a dielectric sleeve.

However, in transmitting the microwave energy into the tissue, the outersurface of the microwave antenna typically may heat up and unnecessarilydesiccate, or even necrose, healthy tissue immediately adjacent theantenna outer surface. This creates a water or tissue phase transition(steam) that allows the creation of a significant additional heattransfer mechanism as the steam escapes from the local/active heatingarea and re-condenses further from the antenna. The condensation back towater deposits significant energy further from the antenna/activetreatment site. This local tissue desiccation occurs rapidly resultingin an antenna impedance mismatch, which both limits power delivery tothe antenna and effectively eliminates steam production/phase transitionas a heat transfer mechanism for tissue ablation.

To prevent the charring of adjacent tissue, several different coolingmethodologies are conventionally employed. For instance, some microwaveantennas utilize balloons which are inflatable around selective portionsof the antenna to cool the surrounding tissue. Thus, the complicationsassociated with tissue damaged by the application of microwave radiationto the region are minimized. Typically, the cooling system and thetissue are maintained in contact to ensure adequate cooling of thetissue.

Other devices attempt to limit the heating of tissue adjacent theantenna by selectively blocking the propagation of the microwave fieldgenerated by the antenna. These cooling systems also protect surroundinghealthy tissues by selectively absorbing microwave radiation andminimizing thermal damage to the tissue by absorbing heat energy.

SUMMARY

The present disclosure provides a system for use with a microwaveantenna including a microwave antenna configured to deliver microwaveenergy from a power source to tissue and a sensor module in operativecommunication with the power source and configured to detect areflectance parameter. The system further includes a jacket adapted toat least partially surround the microwave antenna to define a fluidchannel between the jacket and the microwave antenna. A plurality offluid distribution ports are defined through the jacket and are in fluidcommunication with the fluid channel to permit the flow of fluid throughthe jacket. The system further includes a fluid pumping system operablycoupled to the power source and configured to selectively providecooling fluid to the fluid channel for distribution through the fluiddistribution ports based on the reflectance parameter.

In another embodiment, a system for use with a microwave antennaincludes a microwave antenna configured to deliver microwave energy froma power source to tissue and a temperature sensor operably coupled tothe microwave antenna and configured to detect at least one of a tissuetemperature and an antenna temperature. The system further includes ajacket adapted to at least partially surround the microwave antenna todefine a fluid channel between the jacket and the microwave antenna. Aplurality of fluid distribution ports are defined through the jacket andare in fluid communication with the fluid channel to permit the flow offluid through the jacket. The system further includes a fluid pumpingsystem operably coupled to the power source and configured toselectively provide cooling fluid to the fluid channel for distributionthrough the fluid distribution ports based on a comparison between thedetected temperature and a predetermined temperature.

The present disclosure also provides for a method for impedance matchingduring an ablation procedure. The method includes the initial steps ofapplying microwave energy from an antenna to tissue and detecting areflectance parameter. The method also includes the steps of analyzingthe reflectance parameter to determine an impedance mismatch andselectively expelling an amount of fluid from the antenna into thetissue based on the mismatch. The method further includes the step ofrepeating the step of analyzing the reflectance parameter.

In another embodiment of the present disclosure, a method for regulatingtemperature of tissue undergoing ablation includes the initial steps ofapplying microwave energy from an antenna to tissue and providing atemperature sensor to detect at least one of a tissue temperature and anantenna temperature. The method also includes the steps of comparing thedetected temperature with a predetermined temperature and selectivelyexpelling an amount of fluid from the antenna into the tissue based onthe comparison between the detected temperature and the predeterminedtemperature. The method further includes the step of repeating the stepof comparing the detected temperature with a predetermined temperature.

In another embodiment of the present disclosure, a method for regulatingtemperature of tissue undergoing ablation includes the initial steps ofapplying microwave energy from an antenna to tissue and detecting atleast one of a tissue temperature and an antenna temperature. The methodalso includes the steps of comparing the detected temperature with apredetermined temperature and selectively expelling an amount of fluidfrom the antenna into the tissue based on the comparison between thedetected temperature and the predetermined temperature. The method alsoincludes the step of repeating the step of comparing the detectedtemperature with a predetermined temperature.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentdisclosure will become more apparent in light of the following detaileddescription when taken in conjunction with the accompanying drawings inwhich:

FIG. 1 is a schematic diagram of a microwave antenna assembly accordingto an embodiment of the present disclosure;

FIG. 2 is a perspective view of the microwave antenna assembly of FIG. 1having a conduit defined therein;

FIG. 3 is a cross-sectional view of a microwave antenna according to oneembodiment of the present disclosure;

FIGS. 4A and 4B are enlarged views of the areas of detail of themicrowave antenna of FIG. 3;

FIGS. 4C and 4D are alternative embodiments of the area of detail of themicrowave antenna shown in FIG. 4B;

FIG. 5 is a schematic block diagram of a generator control systemaccording to one embodiment of the present disclosure;

FIG. 6 is a flowchart diagram showing one method for hydrating tissueundergoing treatment according to the present disclosure; and

FIG. 7 is a flowchart diagram showing another method for hydratingtissue undergoing treatment according to the present disclosure.

DETAILED DESCRIPTION

In the drawings and in the description that follows, the term“proximal”, as is traditional, will refer to the end of the apparatusthat is closest to the clinician, while the term “distal” will refer tothe end that is furthest from the clinician.

Microwave or radiofrequency ablation is capable of causing significanttemperature elevations and desiccation of tissue surrounding theapplicator. This elevation of temperature creates a water or tissuephase transition by which steam escapes from the active heating area andrecondenses further from the applicator. In this way, the tissue phasetransition effectively serves as a heat transfer mechanism. As well asadding a new heat transfer mechanism, the movement of water, and,specifically, the loss of water in some volumes of tissue are expectedto affect other tissue properties, such as impedance. Changes in tissuethermal properties directly affects the heat conduction within tissueand changes tissue dielectric properties that lead to changes in thelocation of energy deposition within the targeted, as well as thesurrounding tissues. That is, the condensation back to water depositssignificant energy further from the active heating area. However, thedesiccation of tissue surrounding the applicator effectively eliminatessteam production as a heat transfer mechanism and as a result, thetemperature of the active heating area significantly elevates to causean impedance mismatch.

The present disclosure provides for a system and method to re-hydratetissue undergoing treatment through use of various ablation apparatuses(e.g., a microwave antenna, radiofrequency probe, pump, etc.), whichcompensates for the power imbalance and/or impedance mismatch that areinherent with dynamic tissue changes. In particular, hydration of tissuemay be achieved utilizing cooling systems in which cooling fluid iscirculated through and expelled from a microwave antenna orradiofrequency probe. The following disclosure is directed towards amicrowave antenna application; however, teachings of the presentdisclosure may be applied to other types of ablation devices, such asradiofrequency probes, or even ultrasonic and laser tissue treatmentdevices.

FIG. 1 shows a diagram of an ablation antenna assembly 10 that may beany type of probe suitable for delivering microwave energy and may beused with a cooling system as described herein. The antenna assembly 10generally includes a radiating portion 12 that may be coupled byfeedline 14 (or shaft) via conduit 16 to connector 18, which may furtherconnect the assembly 10 to a power generating source 30 (e.g., agenerator) and a supply pump 40.

Assembly 10 includes a dipole ablation probe assembly. Other antennaassemblies, e.g., monopole or leaky wave antenna assemblies, may also beutilized. Distal portion 22 of radiating portion 12 may include atapered end 26 that terminates at a tip 28 to allow for insertion intotissue with minimal resistance. In those cases where the radiatingportion 12 is inserted into a pre-existing opening, tip 28 may berounded or flat.

Junction member 20 is located between proximal portion 24 and distalportion 22 such that a compressive force may be applied by distal andproximal portions 22, 24 upon junction member 20. Placing distal andproximal portions 22, 24 in a pre-stressed condition prior to insertioninto tissue enables assembly 10 to maintain a stiffness that issufficient to allow for unaided insertion into the tissue whilemaintaining a minimal antenna diameter, as described in detail below.

Feedline 14 electrically connects antenna assembly 10 via conduit 16 togenerator 30 and typically includes a coaxial cable (not explicitlyshown) made of a conductive metal, which may be semi-rigid or flexible.Feedline 14 may also have a variable length from a proximal end ofradiating portion 12 to a distal end of conduit 16 ranging between about1 to 15 inches. The feedline 14 may be constructed of copper, gold,stainless steel or other conductive metals with similar conductivityvalues. The metals may also be plated with other materials, e.g., otherconductive materials, to improve conductivity or decrease energy loss,or for other purposes known in the art.

As shown in FIG. 2, conduit 16 includes a flexible coaxial cable 17 andone or more flexible tubes, namely, inflow tubing 19 and outflow tubing21 for supplying and withdrawing cooling liquid 31 into and out ofradiating portion 12, respectively. Cable 17 includes an inner conductor23 (e.g., wire) surrounded by an insulating spacer 25, which isconcentrically disposed within an outer conductor 27 (e.g., cylindricalconducting sheath). Cable 17 may also include an outer insulating sheath29 surrounding the outer conductor 27. Connector 18 couples the inflowtubing 19 and outflow tubing 21 to the supply pump 40 and the cable 17to the generator 30. The supply pump 40 is coupled to a supply tank 41(FIG. 1) that stores cooling liquid 31 and maintains the liquid at apredetermined temperature (e.g., ambient room temperature). In oneembodiment, the supply tank 41 may include a cooling unit that cools thereturning cooling liquid 31 from the outflow tubing 19.

The cooling fluid 31 may be pumped using positive pressure throughinflow tubing 19. Alternatively, negative pressure may also be used todraw the cooling fluid 31 out of the region through outflow tubing 21.Negative pressure through outflow tubing 21 may be utilized either aloneor in conjunction with positive pressure through inflow tubing 19.Alternatively, positive pressure through inflow tubing 19 may beutilized either alone or in conjunction with negative pressure throughoutflow tubing 21. In pumping the cooling fluid 31, the cooling fluid 31may be passed at a constant flow rate. In another variation, the flowmay be intermittent such that a volume of cooling fluid 31 may be pumpedinto the radiating portion 12 and allowed to warm up by absorbing heatfrom the antenna. Once the temperature of the cooling fluid 31 reaches apredetermined level below temperatures where thermal damage to tissueoccurs, the warmed fluid may be removed and displaced by additionalcooling fluids.

The cooling fluid 31 used may vary depending upon desired cooling ratesand the desired tissue impedance matching properties. Biocompatiblefluids may be included that have sufficient specific heat values forabsorbing heat generated by radio frequency ablation probes, e.g.,liquids including, but not limited to, water, saline, liquidchlorodifluoromethane, etc. In another variation, gases (such as nitrousoxide, nitrogen, carbon dioxide, etc.) may also be utilized as thecooling fluid 31. For example, an aperture defined within the radiatingportion 12 may be configured to take advantage of the cooling effectsfrom the Joule-Thompson effect, in which case a gas, e.g., nitrousoxide, may be passed through the aperture to expand and cool theradiating portion 12. In yet another variation, a combination of liquidsand/or gases, as mentioned above, may be utilized as the cooling medium.

FIG. 3 show a cross-sectional side view and an end view, respectively,of one variation of the antenna assembly 10 (e.g., cooling assembly 100)that may be utilized with any number of conventional ablation probes (orthe ablation probes described herein), particularly the straight probeconfiguration as shown in FIG. 1. Although this variation illustratesthe cooling of a straight probe antenna, a curved or looped ablationprobe may also utilize much of the same or similar principles, asfurther described below.

Cooling assembly 100 includes a cooling handle assembly 102 and anelongated outer jacket 108 extending from handle assembly 102. As willbe described in further detail below, a plurality of fluid distributionports 114 (FIG. 4B) are defined through the thickness of outer jacket108 to facilitate the introduction of cooling fluid 31 from the coolingassembly 100 into surrounding tissue. Outer jacket 108 extends andterminates at tip 110, which may be tapered to a sharpened point tofacilitate insertion into and manipulation within tissue, if necessary.Antenna 104 is positioned within handle assembly 102 such that theradiating portion 106 of antenna 104 extends distally into outer jacket108 towards tip 110. Inflow tubing 19 extends into a proximal end ofhandle body 112 and distally into a portion of outer jacket 108. Outflowtubing 21 extends from within handle body 112 such that the distal endsof inflow tubing 19 and outflow tubing 21 are in fluid communicationwith one another, as described in further detail below.

FIG. 4A shows handle assembly detail 118 from FIG. 3. As shown, handlebody 112 includes proximal handle hub 122, which encloses a proximal endof antenna 104, and distal handle hub 124, which may extend distally toengage outer jacket 108. Proximal handle hub 122 and distal handle hub124 are configured to physically interfit with one another at hubinterface 130 to form a fluid tight seal. Accordingly, proximal handlehub 122 may be configured to be received and secured within acorrespondingly configured distal handle hub 124 (seen in FIG. 3 as amale-female connection). A slide button 116 is disposed on handle body112 and operably coupled to a tube 140 disposed coaxially through atleast a portion of outer jacket 108 (see FIGS. 4B and 4C). Movement ofthe slide button 116 relative to handle body 112, as depicted in FIG. 4Aby bidirectional arrow A, translates corresponding movement of the tube140 relative to an inner surface of outer jacket 108, as depicted inFIG. 4B by bidirectional arrow B, to facilitate the placement of coolingfluid and/or steam into surrounding tissue, as will be discussed infurther detail below.

The distal ends of inflow tubing 19 and outflow tubing 21 may bepositioned within the handle body 112 such that fluid is pumped intohandle body 112 via the supply pump 40 through the inflow tubing 19.Cooling fluid 31 entering the handle body 112 comes into direct contactwith at least a portion of the shaft of the antenna 104 to allow forconvective cooling of the antenna shaft to occur. The cooling fluid 31may be allowed to exit the handle body 112 via the outflow tubing 21. Anadditional inlet tube 126 is positioned within the antenna coolingassembly 100 to extend between the handle body 112 and the radiatingportion 106 (FIG. 4B) of the antenna 104 and a corresponding outlet tube128 may also extend between the handle body 112 and the radiatingportion 106. The proximal end of the inlet tube 126 is in fluidcommunication with the inflow tubing 19 to allow the cooling fluid 31 toflow distally within the outer jacket 108 towards antenna radiatingportion 106 (FIG. 4B). Alternatively, the inlet tube 126 and the outlettube 128 may be omitted from the cooling assembly 100 and the outerjacket 108 may remain in direct fluid communication with the inflowtubing 19 and the outflow tubing 21 such that cooling fluid 31 contactsthe antenna 104 directly along a portion of the length, or a majority ofthe length, or the entire length of the antenna 104. Thus, the coolingassembly 100 is effective in cooling the antenna 104 directly.

FIG. 4B shows outer jacket detail embodiment 120, from FIG. 3. Theillustrated embodiment shows the distal end 132 of inlet tube 126, whichextends distally through outer jacket 108. The opening at distal end 132is positioned within outer jacket 108 near or at the distal end of outerjacket 108 such that distal end 132 opens to fluid channel 134. Thecooling fluid 31 enters fluid channel 134 and fills the volumesurrounding the radiating portion 106 and surrounding at least a portionof the antenna 104. As cooling fluid 31 enters fluid channel 134, thecooling fluid 31 is withdrawn through a distal opening in outlet tube128, which is located proximally of distal end 132 to allow forincreased convective cooling between the cooling fluid 31 and theantenna 104.

The cooling fluid 31 is pumped using positive pressure through inlettube 126. Alternatively, negative pressure may also be used to draw thefluid out of the region through outlet tube 128. Negative pressurethrough outlet tube 128 may be utilized either alone or in conjunctionwith positive pressure through inlet tube 126. Alternatively, positivepressure through inlet tube 126 may be utilized either alone or inconjunction with negative pressure through outlet tube 128.

The cooling fluid 31 used may vary depending upon desired cooling ratesand the desired tissue impedance matching properties. Biocompatiblefluids having sufficient specific heat values for absorbing heatgenerated by microwave ablation antennas may be utilized, e.g., liquidsincluding, but not limited to, water, saline, Fluorinert ®, liquidchlorodifluoromethane, etc. (As is well-known, the material sold underthe trademark Fluorinert is a perfluorocarbon fluid distributedcommercially by Minnesota Mining and Manufacturing Company (3M), St.Paul, Minn., USA.)

The illustrated embodiment in FIG. 4B shows tube 140 and a plurality offluid distribution ports 114 defined through the thickness of the outerjacket 108. The fluid distribution ports 114 enable cooling fluid 31 tobe expelled from the fluid channel 134 into and/or proximate the targettissue. Tube 140 is disposed coaxially through at least a portion ofouter jacket 108 such that fluid communication between one or more fluiddistribution ports 114 and fluid channel 134 is selectively interrupted.More specifically, as tube 140 is moved from a distal most position (seeFIGS. 4B and 4C) proximally relative to outer jacket 108 bycorresponding proximal movement of slide button 116, an increasingnumber of fluid distribution ports 114 are exposed to fluid channel 134from a distal end of fluid channel 134 toward a proximal end of fluidchannel 134, to permit cooling fluid 31 to be expelled via the exposedfluid distribution ports 114 into and/or proximate the target tissue.Similarly, distal movement of slide button 116 relative to handle body112 causes distal movement of tube 140 to interrupt fluid communicationbetween fluid distribution ports 114 and fluid channel 134 from aproximal end thereof toward a distal end thereof. In this manner, a usermay manipulate the slide button 116 relative to the handle body 112 tocontrol the placement of cooling fluid and/or steam as desired ordepending on the size of the ablation. In some embodiments, the fluiddistribution ports 114 may be microporous, macroporous, or anycombination thereof. The higher the porosity, the more freely thecooling fluid 31 will flow through the outer jacket 108. The fluiddistribution ports 114 may be defined through the outer jacket 108 alongthe entire length thereof. Alternatively, the fluid distribution ports114 may only be defined through the portion of the outer jacket 108 thatwill be adjacent the ablation region (e.g., a distal end of theradiating portion 106). The cooling fluid 31 flows outwardly through thefluid distribution ports 114 as shown by the arrows extending outwardlytherefrom. Alternatively, one or more of the fluid distribution ports114 may be defined at an angle with respect to the surface of the outerjacket 108 (not explicitly illustrated) such that the cooling fluid 31may flow outwardly in various radial directions (e.g., proximal, distal,etc.).

In some embodiments, cooling assembly 100 may include passive-type plugsor seals (not explicitly shown) to passively seal each fluiddistribution port 114. The seals may be expanded outward by positivefluid pressure communicated through the fluid distribution ports 114 toallow cooling fluid 31 to be expelled from the cooling assembly 100. Inthis way, cooling fluid 31 may remain circulated within the fluidchannel 134 until the supply pump 40 creates additional positive fluidpressure to expand the seals outward, thereby permitting cooling fluid31 to exit the fluid channel 134 via the fluid distribution ports 114.

In some embodiments, the cooling assembly 100 may be configured toselectively inject cooling fluid 31 into the surrounding tissue throughany one or more specific fluid distribution ports 114. That is, coolingfluid 31 may be injected into the surrounding tissue from any port orgroup of ports positioned about the circumference of the outer jacket108. In this configuration, the cooling assembly 100 may include one ormore additional inflow tubes (not explicitly shown) in direct fluidcommunication with a specific port or specific group of ports. As such,the controller 34 may cause the supply pump 40 to pump cooling fluid 31through specific inflow tubes and/or specific groups of inflow tubesinto and/or proximate the surrounding tissue via specific ports orspecific groups of ports. In this way, cooling fluid 31 may be targetedproximally, distally, or in a specific radial direction.

FIG. 4C shows an alternative embodiment of inlet tube 126 shown as ahelical shape extending distally through outer jacket 108. In thisconfiguration, inlet tube 126 is in contact with the radiating portion106 to facilitate faster heating of the cooling fluid within inlet tube126 such that steam may be expelled from a plurality of ports 127disposed through inlet tube 126.

In some embodiments, as shown in FIG. 4D, one or more infusion inlettubes 150 may be disposed coaxially through outer jacket 108 to provideinfusion fluid (not shown) directly from the supply pump 40, as opposedto cooling fluid 31 supplied via inlet tube 126, such that infusionfluid and cooling fluid circulate separately within the antenna assembly10. In this scenario, additional inflow tubing (not shown) is disposedin fluid communication between the supply pump 40 and infusion inflowtubes 150 and supplies infusion fluid to the infusion inflow tubes 150using positive pressure from the supply pump 40. Infusion inlet tubes150 are in fluid communication with one or more fluid distribution ports114 such that positive pressure from the supply pump 40 causes theinfusion fluid in the infusion inflow tubes 150 to be expelled from oneor more fluid distribution ports 114 and into and/or proximate thetarget tissue. The embodiment in FIG. 4D may be particularly suitablefor radiofrequency ablation.

FIG. 5 shows a schematic block diagram of the generator 30 operablycoupled to the supply pump 40. The supply pump 40 is, in turn, operablycoupled to the supply tank 41. The generator 30 includes a controller34, a power supply 37, a microwave output stage 38, and a sensor module32. The power supply 37 provides DC power to the microwave output stage38 which then converts the DC power into microwave energy and deliversthe microwave energy to the radiating portion 106. The controller 34includes a microprocessor 35 having a memory 36 which may be volatiletype memory (e.g., RAM) and/or non-volitile type memory (e.g., flashmedia, disk media, etc.). The microprocessor 35 includes an output portconnected to the supply pump 40, which allows the microprocessor 35 tocontrol the output of cooling fluid 31 from the supply pump 40 to thecooling assembly 100 according to either open and/or closed control loopschemes. In the illustrated embodiment, the microprocessor 35 alsoincludes an output port connected to the power supply 37 and/ormicrowave output stage 38 that allows the microprocessor 35 to controlthe output of the generator 30 according to either open and/or closedcontrol loop schemes. Further, the cooling assembly 100 may includesuitable input controls (e.g., buttons, activators, switches, etc.) formanually controlling the output of the supply pump 40. Specifically, theinput controls may be provided with leads (or wireless) for transmittingactivation signals to the controller 34. The controller 34 then signalsthe supply pump 40 to control the output of cooling fluid 31 from thesupply tank 41 to the cooling assembly 100. In this way, clinicians maymanually control the supply pump 40 to cause cooling fluid 31 to beexpelled from the cooling assembly 100 into and/or proximate thesurrounding tissue.

A closed loop control scheme generally includes a feedback control loopwherein the sensor module 32 provides feedback to the controller 34(i.e., information obtained from one or more sensing mechanisms forsensing various tissue and/or antenna parameters, such as tissueimpedance, antenna impedance, tissue temperature, antenna temperature,output current and/or voltage, etc.). The controller 34 then signals thesupply pump 40 to control the output thereof (e.g., the volume ofcooling fluid 31 pumped from the supply tank 41 to the cooling assembly100). The controller 34 also receives input signals from the inputcontrols of the generator 30 and/or antenna assembly 10. The controller34 utilizes the input signals to adjust the cooling fluid 31 output ofthe supply pump 40 and/or the power output of the generator 30.

The microprocessor 35 is capable of executing software instructions forprocessing data received by the sensor module 32, and for outputtingcontrol signals to the generator 30 and/or supply pump 40, accordingly.The software instructions, which are executable by the controller 34,are stored in the memory 36 of the controller 34.

The controller 34 may include analog and/or logic circuitry forprocessing the sensed values and determining the control signals thatare sent to the generator 30 and/or supply pump 40, rather than, or incombination with, the microprocessor 35. The sensor module 32 mayinclude a plurality of sensors (not explicitly shown) strategicallylocated for sensing various properties or conditions, e.g., tissueimpedance, antenna impedance, voltage at the tissue site, current at thetissue site, tissue temperature, antenna temperature, etc. The sensorsare provided with leads (or wireless) for transmitting information tothe controller 34. The sensor module 32 may include control circuitrythat receives information from multiple sensors, and provides theinformation and the source of the information (e.g., the particularsensor providing the information) to the controller 34.

When coupling electromagnetic radiation such as microwaves from a sourceto an applicator, in order to maximize the amount of energy transferredfrom the source (microwave generator) to the load (surgical implement),the line and load impedances should match. If the line and loadimpedances do not match (e.g., an impedance mismatch) a reflected wavemay be created that can generate a standing wave, which contributes to apower loss associated with the impedance mismatch. As used herein, “loadimpedance” is understood to mean the impedance of the radiating portion12 and “line impedance” is understood to mean the impedance of thefeedline 14.

In some embodiments, the controller 34 is configured to control thecooling fluid 31 output from the supply pump 40 to the antenna assembly10 based on a reflectance parameter, such as a mismatch detected betweenthe load impedance and the line impedance. Such an impedance mismatchmay cause a portion of the power, so called “reflected power,” from thegenerator 30 to not reach the tissue site and cause the power delivered,the so called “forward power,” to vary in an irregular or inconsistentmanner. It is possible to determine the impedance mismatch by measuringand analyzing the reflected and forward power. In particular, thegenerator 30 measures energy delivery properties, namely the forwardpower, and dynamically adjusts the cooling fluid 31 output of the supplypump 40 to compensate for a detected mismatch between the line impedanceand the load impedance. That is, upon detection of an impedancemismatch, additional cooling fluid 31 is pumped through inflow tubing 19and into the fluid channel 134 using positive pressure from the supplypump 40. This positive pressure causes additional fluid pressure in thefluid channel 134, which in turn, causes cooling fluid 31 to flowthrough the fluid distribution ports 114 (e.g., by expanding the sealsoutward) into and/or proximate the surrounding tissue. In this manner,the cooling fluid 31 effectively re-hydrates surrounding tissue togenerate additional steam. This generation of additional steam allowsfor the transfer of heat away from the target tissue site for theduration of the procedure. The resulting drop in tissue temperature (ormore specifically, a change in a dielectric constant el of the tissuesurrounding the antenna) effectively lowers the load impedance to matchthe line impedance, thereby optimizing energy delivery to the targettissue site. Other reflectance parameters include reflectancecoefficient, standing wave ratio (SWR), and reflectance loss.

In operation, the sensor module 32 is coupled to the microwave outputstage 37 and is configured to measure a reflectance parameter. Thesensor module 32 may include one or more directional couplers or othervoltage and current sensors that may be used to determine voltage andcurrent measurements as well as the phase of the voltage and currentwaveforms. The voltage and current measurements are then used by thesensor module 32 to determine the reflectance parameter. The sensormodule 32 converts the measured parameter into corresponding low levelmeasurement signals (e.g., less than 5 V) which are transmitted to thecontroller 34.

The controller 34 accepts one or more measurements signals indicative ofpower delivery, namely, the signals indicative of the reflectanceparameter. The controller 34 analyzes the measurement signals anddetermines an impedance mismatch based on the reflectance parameter. Thecontroller 34 thereafter determines whether any adjustments to theoutput of the supply pump 40 have to be made to adjust (e.g.,re-hydrate) the surrounding tissue to compensate for the mismatch inimpedance based on the reflectance parameter. Additionally, thecontroller 34 may also signal the microwave output stage 38 and/or thepower supply 37 to adjust output power based on the reflectanceparameter.

FIG. 6, in conjunction with FIGS. 3, 4A, 4B, and 5, illustrates a method200 for selectively re-hydrating tissue undergoing treatment accordingto one embodiment. In step 210, energy from the generator 30 is appliedto tissue via the antenna 104 to heat a target treatment area. In step235, one or more reflectance parameters are detected by the sensormodule 32 (e.g., using sensors) and communicated to the controller 34for storage in the memory 36. In the illustrated embodiment, thereflectance parameters detected in step 235 include a load impedance(detected in step 220) and a line impedance (detected in step 230). Instep 240, the microprocessor 35 compares the load impedance to the lineimpedance. If the load impedance and the line impedance are not at leastsubstantially equivalent in step 250, the microprocessor 35 outputs acontrol signal to the supply pump 40 in step 260 to cause cooling fluid31 to be expelled from the cooling assembly 100 into and/or proximatethe surrounding tissue. If the load impedance and line impedance aresubstantially equivalent in step 250, step 240 is repeated. The method200 may loop continuously throughout the duration of the procedure tore-hydrate the target tissue and generate additional steam as a heattransfer mechanism. The resulting drop in tissue temperature (or changein dielectric constant el of the tissue surrounding the antenna) acts toimprove energy delivery to the target tissue by facilitating animpedance match between the line and the load.

FIG. 7, in conjunction with FIGS. 3, 4A, 4B, and 5, illustrates a method300 for selectively re-hydrating tissue undergoing treatment accordingto another embodiment. In step 310, energy from the generator 30 isapplied to tissue via the antenna 104 to heat a target treatment area.In step 320, a tissue temperature and/or an antenna temperature isdetected by the sensor module 32 (e.g., using an optical temperaturesensor) and communicated to the controller 34 for storage in the memory36. In step 330, the microprocessor 35 compares the detected temperatureto a predetermined temperature (e.g., about 104° C.). If the detectedtemperature is greater than or equal to the predetermined temperature instep 340, the microprocessor 35 outputs a control signal to the supplypump 40 in step 350 to cause cooling fluid to be expelled from thecooling assembly 100 into and/or proximate the surrounding tissue. Ifthe detected temperature is less than the predetermined temperature instep 340, step 330 is repeated. The method 300 may loop continuouslythroughout the duration of the procedure to re-hydrate the target tissueand generate additional steam as a heat transfer mechanism. Theresulting drop in tissue temperature acts to improve energy delivery bymaintaining the target tissue site at a temperature below a temperatureat which significant tissue dehydration may occur.

In some embodiments, the disclosed methods may be extended to othertissue effects and energy-based modalities including, but not limitedto, ultrasonic and laser tissue treatments. The methods 200 and 300 arebased on impedance measurement and monitoring and temperaturemeasurement and monitoring, respectively, but other tissue and energyproperties may be used to determine state of the tissue, such ascurrent, voltage, power, energy, phase of voltage and current. In someembodiments, the method may be carried out using a feedback systemincorporated into an electrosurgical system or may be a stand-alonemodular embodiment (e.g., removable modular circuit configured to beelectrically coupled to various components, such as a generator, of theelectrosurgical system).

While several embodiments of the disclosure have been shown in thedrawings and/or discussed herein, it is not intended that the disclosurebe limited thereto, as it is intended that the disclosure be as broad inscope as the art will allow and that the specification be read likewise.Therefore, the above description should not be construed as limiting,but merely as exemplifications of particular embodiments. Those skilledin the art will envision other modifications within the scope and spiritof the claims appended hereto.

What is claimed is:
 1. A system for use with a microwave antenna, comprising: a microwave antenna configured to deliver microwave energy from a power source to tissue; a sensor module in operative communication with the power source and configured to detect a reflectance parameter; a jacket defining a plurality of fluid distribution ports therethrough and adapted to at least partially surround the microwave antenna to define a fluid channel therebetween, the plurality of fluid distribution ports in fluid communication with the fluid channel and configured to permit the flow of fluid therethrough; and a fluid pumping system operably coupled to the power source and configured to selectively provide cooling fluid to the fluid channel for distribution through the fluid distribution ports based on the reflectance parameter.
 2. A system according to claim 1, wherein the sensor module is further configured to provide information to a comparator relating to the reflectance parameter.
 3. A system according to claim 2, wherein the reflectance parameter is selected from the group consisting of a reflectance coefficient, a standing wave ratio, a reflectance loss, or an impedance mismatch.
 4. A system according to claim 1, wherein the fluid is selected from the group consisting of water, saline, and a water-based biological solution.
 5. A system according to claim 1, wherein the jacket is adapted to at least partially surround a radiating portion of the microwave antenna.
 6. A system according to claim 1, wherein the sensor module is further configured to detect at least one of an energy property and a tissue property and provide information relating thereto back to the power source for controlling the fluid pumping system based on the detected property.
 7. A system according to claim 1, further comprising a tube disposed coaxially through at least a portion of the jacket and movable relative thereto to selectively interrupt the fluid communication between at least one of the plurality of fluid distribution ports and the fluid channel.
 8. A system according to claim 1, further comprising a helical inlet tube adapted to at least partially surround a radiating portion of the microwave antenna and including at least one port configured to selectively provide cooling fluid to the fluid channel.
 9. A system according to claim 1, further comprising: at least one infusion inlet tube disposed coaxially through the jacket and in fluid communication with the fluid pumping system and wherein at least one of the fluid distribution ports is configured to selectively infuse fluid from the fluid pumping system for distribution therethrough.
 10. A system for use with an ablation device, comprising: an ablation device configured to deliver energy from a power source to tissue; a temperature sensor operably coupled to the ablation device and configured to detect at least one of a tissue temperature and a device temperature; a jacket defining a plurality of fluid distribution ports therethrough and adapted to at least partially surround the ablation device to define a fluid channel therebetween, the plurality of fluid distribution ports in fluid communication with the fluid channel and configured to permit the flow of fluid therethrough; and a fluid pumping system operably coupled to the power source and configured to selectively provide cooling fluid to the fluid channel for distribution through the fluid distribution ports based on a comparison between the detected temperature and a predetermined temperature.
 11. A system according to claim 10, wherein the predetermined temperature is about 104° C.
 12. A system according to claim 10, wherein the fluid pumping system is configured to pump cooling fluid through at least one of the plurality of fluid distribution ports if the detected temperature is greater than the predetermined temperature.
 13. A cooling system according to claim 10, wherein the sensor module is further configured to provide information to a comparator relating to the detected temperature and the predetermined temperature.
 14. A method for impedance matching during an ablation procedure, the method comprising: applying microwave energy from an antenna to tissue; detecting a reflectance parameter; analyzing the reflectance parameter to determine an impedance mismatch; selectively expelling an amount of fluid from the antenna into the tissue based on the mismatch; and repeating the step of analyzing the reflectance parameter.
 15. A method according to claim 14, wherein the selectively expelling step further includes the step of providing a plurality of fluid distribution ports defined through an outer surface of the antenna to permit the flow of fluid therethrough into the tissue.
 16. A method according to claim 14, wherein the fluid of the selectively expelling step is expelled from a radiating portion of the ablation antenna.
 17. A method according to claim 14, wherein the selectively expelling step further includes the step of actuating a tube disposed coaxially through the antenna to control the amount of fluid expelled from the antenna.
 18. A method for regulating temperature of tissue undergoing ablation, the method comprising: applying microwave energy from an antenna to tissue; detecting at least one of a tissue temperature and an antenna temperature; comparing the detected temperature with a predetermined temperature; selectively expelling an amount of fluid from the antenna into the tissue based on the comparison between the detected temperature and the predetermined temperature; and repeating the step of comparing the detected temperature with a predetermined temperature.
 19. A method according to claim 18, wherein the selectively expelling step further includes the step of selectively expelling the fluid when the detected temperature is greater than the predetermined temperature.
 20. A method according to claim 18, wherein the selectively expelling step further includes selectively expelling the fluid when the detected temperature is substantially equal to the predetermined temperature. 